ISTANBUL (Reuters) – As the magnitude of an earthquake in a television advert gradually mounts, the stone letters ISTANBUL crack, and then crumble to dust.

If it seems alarmist, builder Cuneyt Kilic, whose company AKS Anatolian Housing is behind the graphic depicting the collapse of Turkeyâ€™s largest city, says it is merely realistic.

Many scientists agree the question is not if, but when in the next three decades a major earthquake will hit Istanbul, the former seat of the Byzantine and Ottoman empires and source of more than half Turkeyâ€™s industrial output.

Turkeyâ€™s top seismologist said in November â€œthe big oneâ€ could kill more than 100,000 people.

Turkey lies on a major fault line and has had 90 earthquakes higher than magnitude 5 since 1903, including one in August 1999 when nearly 18,000 people were killed.

Of those deaths 1,000 were in Istanbul, and many were blamed on sub-standard buildings thrown up by a construction industry rife with corruption.

â€œAt the moment of the earthquake, coming from under ground, thereâ€™s a sound, itâ€™s like a washing machine on a spin cycle,â€ recalled grocer Gungor Dincer, who survived that quake.

An earthquake in Istanbul in 1509, accompanied by floods and weeks of aftershocks, was so devastating it was described as the â€œsmall doomsday,â€ opening fissures in the ground, bringing down the city walls and knocking over every minaret in the city, according to various accounts.

The city of 13 million has been hit by quakes since then, but the epicentre has not been in Istanbul since 1894, or according to some experts 1766, when the quake was accompanied by a tsunami.

â€œNot Scaremongeringâ€

â€œWeâ€™re not scaremongering,â€ Kilic, deputy head of AKS told Reuters, saying people should be aware of the predictions. Some clearly are, as AKS has already sold 60 percent of a new development of quake-resistant steel-built houses due for handover this year.

Concern has been mounting. A series of small earthquakes filled newspapers in recent weeks with expert predictions on when the next big one would come.

In October local media quoted National Earthquake Council Chairman Haluk Eyidogan criticising authorities for failing to enforce rules on construction and structural inspections.

Istanbulâ€™s governor acknowledged that many of the cityâ€™s buildings would not withstand a large quake; professors at one leading university recently resolved to stop talking to the press to avoid stirring panic.

But if the fear of a quake is proving good business for some, Istanbulâ€™s ability to protect the less wealthy is a political concern.

An earthquake plan was launched after the 1999 quake near Istanbul, but experts say no action has been taken on the studies commissioned.

One such study completed in 2004 shows that of 16,000 buildings in one vulnerable area 2,300 were declared very high risk — or expected to collapse in a quake. Two similar studies are due to be completed in other areas next year.

â€œNothing has been done yet,â€ said Haluk Sucuoglu, professor of civil engineering and member of the National Earthquake Council.

â€œThereâ€™s no political motivation related to this. They claim they are motivated but we donâ€™t see any action,â€ he added.

â€œ$10 BILLION, 10 YEARSâ€

Amid such criticism, Istanbul recently launched a major disaster simulation exercise to reassure the public.

Turkey in October 2005 signed a $400 million plan with the World Bank to improve its preparation for an emergency, strengthen facilities for earthquake resistance and ensure better enforcement of building codes.

That sum compares with a terse estimate from Istanbulâ€™s Bas for preparing the city for a quake: â€œ$10 billion, 10 years.â€

To invest that would be tricky in a heavily indebted European Union-applicant country where the International Monetary Fund keeps a close eye on spending.

And in a city which receives tens of thousands of rural migrants a year, and where luxury malls coexist with shanty towns, upscale buildings like those Kilic sells can only be aimed at the minority.

In Turkey, where the underground economy is huge, almost a third of the construction industry in unregistered, according to an estimate from the head of Turkeyâ€™s Cement Producersâ€™ Association Adnan Ignebekcili.

That leaves the rest in the city to weigh their options: refit buildings, pull them down, or trust to fate.

Halim Sahin, an Istanbul real estate agent, said only 20 to 30 percent of his clients even ask about how safe a building would be in an earthquake.

â€œThereâ€™s fatalism. People think you could die in a car crash, or of a heart attack … As a society weâ€™re fatalists.â€